There has been proposed several methods for producing 1,4-dihydroxy-2-naphthoic acid which is useful as an intermediate in the production of dyes, pigments and photographic agents.
For example, J. Am. Chem. Soc., vol. 64, 798 (1942) reports a method for producing 1,4-dihydroxy-2-naphthoic acid by using phthalic acid and a succinate. J. Prakt. Chem., vol. (2)62, p. 30 (1900) reports that the target naphthoic acid is synthesized by reacting 1,4-dihydroxynaphthalene with alcoholic sodium hydroxide or alcoholic potassium hydroxide in an alcohol solvent to form a sodium or potassium salt thereof, drying the obtained product in a hydrogen gas stream, allowing the crystals thus obtained to reaction with carbon dioxide under increased pressure of carbon dioxide gas at 170.degree. C. for 20 to 30 hours, and then subjecting the reaction mixture to salting out with diluted hydrochloride acid.
In recent years, JP-A-57-126443 and JP-A-57-128655 propose each a method for carboxylating 1,4-dihydroxynaphthalene with carbon dioxide gas in an organic medium in the presence of potassium carbonate anhydride in the form of fine particles. JP-A-59-141537 and JP-A-60-104037 also propose each a method for carboxylating 1,4-dihydroxynaphthalene with carbon dioxide gas in the presence of an alkali metal compound and water. The term "JP-A" as used herein means an "unexamined published Japanese patent application".
However, the method for producing 1,4-dihydroxy-2-naphthoic acid from phthalic acid and a succinate requires a long time and a complicated procedure. In the case of the method comprising isolating an alkali metal salt of 1,4-dihydroxynaphthalene and then carboxylating with carbon dioxide gas, the alkali metal salt of 1,4-dihydroxynaphthalene is highly unstable and a large amount of by-products are formed, thereby decreasing the yield of the desired product. In addition, there are a number of difficulties in the embodiment of this method on an industrial scale.
In the case of the methods described in JP-A-57-126443 and JP-A-57-128655, it is necessary to use highly hygroscopic fine particles of potassium carbonate anhydride and to carry out the reaction at a high temperature under an increased pressure for a long period of time while maintaining the moisture content at a level of 0.5% or less. In addition, a complicated procedure is needed in order to isolate the desired 1,4-dihydroxy-2-naphthoic acid from the reaction mixture.
The methods described in JP-A-59-141537 and JP-A-60-104037 can establish only a low conversion ratio and it is therefore needed to recover the starting material. In addition, it is necessary to rapidly cool the reaction mixture after the completion of the reaction, since the cooling rate affects the yield.
Thus, although there have been proposed several methods for producing 1,4-dihydroxy-2-naphthoic acid, it is hard to say that they are advantageous from an industrial viewpoint. Therefore, it has been urgently required to establish an industrially advantageous method for producing 1,4-dihydroxy-2-naphthoic acid.